The invention relates to radiotherapy, and more particularly relates to stereotactic radiotherapy. In its most immediate sense, the invention relates to intracranial stereotactic radiotherapy.
In radiotherapy, a treatment beam of high-energy radiation is made incident on to a tumor that is to be destroyed. In intracranial stereotactic radiotherapy, an image-guided radiotherapy apparatus (“IGRT” apparatus) is used to destroy a brain tumor. An IGRT apparatus includes an imaging system such as a cone-beam computed tomography system (a “CBCT” system) and a linear accelerator. The imaging system is used to acquire an image of the tumor and the linear accelerator is used to produce the treatment beam, which is aimed at the tumor to destroy it.
In order to carry out intracranial stereotactic radiotherapy successfully, two localizations must occur. One of these localizations is carried out by the imaging modality; the e.g. CBCT image localizes the tumor within the patient's head. The other required localization is the localization of the patient's head within the coordinate system of the IGRT apparatus. This is carried out using an alignment device that is recognized by the IGRT apparatus or by equipment that is used together with it.
Before the patient's treatment begins, the alignment device is mounted to the patient and a computed tomography study (a “simulation”) is carried out to acquire an image of the patient's head. During this image acquisition, the alignment device is used to register the precise location and orientation of the patient's head. Then, the information acquired during this simulation is used to develop a treatment plan for irradiating the tumor. To treat a patient who has been placed within the IGRT apparatus, the alignment device is used again to localize the patient's actual head position within the coordinate system of the IGRT apparatus and to place the patient's head in a location that precisely matches the position and orientation of the patient's head during the simulation procedure. And, since the position of the tumor within the patient's head is known from the image acquired during simulation, the treatment plan can be executed to destroy the tumor with little or no destruction of healthy tissue that surrounds the tumor.
The alignment device must operate with a high degree of repeatability because the localization of the patient within the IGRT apparatus must always be precise. If the alignment device works differently during patient imaging then during patient treatment, or if it works differently during successive treatments, the beam of ionizing radiation will be inaccurately aimed. This will cause unnecessary destruction of healthy tissue and insufficient destruction of tumor tissue.
In one category of alignment devices, a component with a known structure is physically attached to the patient's head and interacts with apparatus that registers the location of the component. This permits the location of the patient's head to be accurately determined. For example, the SonArray device manufactured by Varian has a bite plate that is held in the patient's mouth. Proper repeat positioning of the patient using the SonArray device requires the patient to bite with consistent pressure. This can be difficult. In addition, the SonArray device can be uncomfortable in use, especially with patients who have had teeth extracted (as is the case with many head and neck radiotherapy patients). Furthermore, if the patient swallows his or her saliva, the SonArray device can move with respect to the patient, causing the position of patient's head to be mis-registered within the coordinate system of the IGRT apparatus.
In the AlignRT device manufactured by Vision RT, the position of the patient is determined by image processing. The AlignRT device acquires images of the patient's head using two cameras whose locations and orientations are precisely known. After the two images are acquired, the device identifies patient features that appear in both images and then reconstructs 3D surface data to localize the patient's head using triangulation. If the patient loses weight or the pattern of the patient's facial hair changes (both conditions are often encountered with chemotherapy), the precision with which the patient's head is localized can be adversely affected.
It would be advantageous to provide a cranial alignment device for use in intracranial stereotactic radiotherapy that is comfortable, that does not require effort from the patient, and that operates with a high degree of repeatability even if the patient loses or gains weight, and even if the patient's hair pattern changes (hair loss occurs in patients who undergo chemotherapy).
One object of the invention is to provide a method for reproducibly positioning a patient's head, and a cranial alignment device for use in intracranial stereotactic radiotherapy, that are comfortable for the patient, that do not require the patient to exert effort, and that operate with a high degree of repeatability even if the patient's surface anatomy changes (as by gain or loss of weight or hair loss).
Another object is, in general, to improve on known devices and methods of this general type.
The invention proceeds from the realization that for any patient, the shapes of the dorsum and alae of the patient's nose do not change when the patient gains or loses weight. Furthermore, these locations seldom have substantial hair growth. Thus, an alignment device that is mounted to the patient's head using a custom shaped nosepiece that mates with the dorsum and alae of the patient's nose will always fit on the patient's head in precisely the same way and in a rigid manner. This will be true whether the patient gains or loses weight or whether the patient loses hair.
A device in accordance with the invention has two earpieces and a front frame that is connected between them. These components are dimensioned to fit upon a patient's face with the front frame in front of the patient's eyes and each earpiece engaging behind one of the patient's ears. The device further has a nosepiece that is custom shaped to mate with the dorsum and alae of the patient's nose and that is detachably securable to the front frame. The device also has a plurality of infrared-reflecting markers mounted on the front frame.
A device in accordance with the invention is worn on the patient's head like a pair of eyeglasses. The patient is not required to exert any effort to keep the device in place, and changes in the patient's weight and hair patterns do not affect the way the device fits on the patient's head. A conventional optical tracking system such as is conventionally used with IGRT apparatus can be used to register with six-degrees-of-freedom (translation and rotation) the position of the device—and therefore the position of the patient's head—in the coordinate system of the IGRT apparatus.
A device in accordance with the invention is inexpensive and simple to make and to fit to a patient. And, no additional equipment is needed because an optical tracking system will likely be available anyway.
Advantageously, the infrared-reflecting markers are not coplanar and are positioned asymmetrically in two groups, each group being associated with one of the patient's eyes. Such a pattern minimizes the likelihood that the optical tracking system will improperly localize the device within the coordinate system of the IGRT apparatus.
In a method in accordance with the invention, a nosepiece that mates with the dorsum and alae of the patient's nose is created. The nosepiece is attached to a fixture that is adapted for mounting on the patient's head, and the fixture is mounted on the patient's head.